Lacking Superoxide Dismutase Research Articles

Unbalance between Pyridine Nucleotide Cofactors in The SOD1 Deficient Yeast Saccharomyces cerevisiae Causes Hypersensitivity to Alcohols and Aldehydes.

Alcohol and aldehyde dehydrogenases are especially relevant enzymes involved in metabolic and detoxification reactions that occur in living cells. The comparison between the gene expression, protein content, and enzymatic activities of cytosolic alcohol and aldehyde dehydrogenases of the wild-type strain and the Δsod1 mutant lacking superoxide dismutase 1, which is hypersensitive to alcohols and aldehydes, shows that the activity of these enzymes is significantly higher in the Δsod1 mutant, but this is not a mere consequence of differences in the enzymatic protein content nor in the expression levels of genes. The analysis of the NAD(H) and NADP(H) content showed that the higher activity of alcohol and aldehyde dehydrogenases in the Δsod1 mutant could be a result of the increased availability of pyridine nucleotide cofactors. The higher level of NAD+ in the Δsod1 mutant is not related to the higher level of tryptophan; in turn, a higher generation of NADPH is associated with the upregulation of the pentose phosphate pathway. It is concluded that the increased sensitivity of the Δsod1 mutant to alcohols and aldehydes is not only a result of the disorder of redox homeostasis caused by the induction of oxidative stress but also a consequence of the unbalance between pyridine nucleotide cofactors.

Ecotoxicity testing of paraquat metabolites degraded by filamentous fungi in model organism

Paraquat has been intensively used worldwide for several decades for the purpose of weed control in profit crop plantation. This leads to the accumulation of the herbicide and its metabolites in the environment. One promising method to reduce and/or eliminate the paraquat-contaminants is via microbial bioremediation. Filamentous fungi, Aspergillus tamarii PRPY-2, isolated from rubber tree plantation in the northern part of Thailand exhibited the ability to degrade paraquat in liquid media at laboratory scale. Thus, utilization of this species in paraquat-contaminated sites is potentially feasible. However, metabolites generated during biodegradation processes are possibly more toxic than the parent compound. Hence, before introducing this microbe into the environment, it is necessary to ensure that metabolites have no adverse effects on the ecosystem. The present work focuses on the study of the toxic effects of paraquat metabolites on the eukaryote model organism using Saccharomyces cerevisiae of wild type and five mutant strains. The relation between paraquat degradation and growth of fungi was firstly performed. Ecotoxicity testing was done via chemo-genetic screening method. Oxidative stress-related enzyme, superoxide dismutase of S. cerevisiae was also verified. The results illustrated that fungi could degrade 100% of paraquat in Czapeck Dox liquid medium within 21 days. Ecotoxicity data indicated that all yeast strains grew better in a medium containing paraquat metabolites than the one containing parent compound. Among them, mutant lacking superoxide dismutase (SOD1) gene was the most affected strain. Moreover, enzyme activity of yeast cells exposed to paraquat metabolites was found to be lower than that exposed to parent compound. In summary, metabolites degraded by A. tamarii are less toxic to model organism than paraquat. Therefore, the utilization of this species for remediation purpose was found to be safe for the environment.

Superoxide dismutase C affects Dictyostelium contractile vacuole biogenesis and function

Dictyostelium cells cope with hypo-osmotic stress with a contractile vacuole (CV) system, which consists of one or two vacuoles that cyclically charge and discharge. Uniquely, a F-Actin remodeling dependent minimal mixing of the CV membrane components with the target plasmalemma during the fusion and the dischargement warrants the integrity of the CV bladder for an efficient next CV cycle. The effect of hypo-osmotic stress on F-Actin remodeling activity, however, is currently not well understood. Dictyostelium cells increase the level of intracellular superoxide level in response to hypo-osmotic stress, which in turn activates redox-sensitive Ras proteins, but not Akt, which is one of the Ras downstream targets and a major regulator of F-Actin remodeling. However, Akt is not insulated from the active Ras in cells lacking Superoxide dismutase C (SodC). We report here that sodC- cells were compromised in the CV structure and function and the attenuation of Ras/PI3K/Akt signaling in several independent means significantly improved the compromised CV structure but not the function. Interestingly, when sodC- cells were treated with 5-(N,N-Dimethyl) amiloride hydrochloride (EIPA), an inhibitor of sodium proton exchanger (NHE), both the structure and the function of the CV improved. Thus, a proper CV biogenesis in sodC- cells was insufficient to restore their CV function, which in turn indicates the presence of an additional target for SodC and EIPA that modulates CV function.

Sublethal Paraquat Confers Multidrug Tolerance in Pseudomonas aeruginosa by Inducing Superoxide Dismutase Activity and Lowering Envelope Permeability.

Stressors and environmental cues shape the physiological state of bacteria, and thus how they subsequently respond to antibiotic toxicity. To understand how superoxide stress can modulate survival to bactericidal antibiotics, we examined the effect of intracellular superoxide generators, paraquat and menadione, on stationary-phase antibiotic tolerance of the opportunistic pathogen, Pseudomonas aeruginosa. We tested how pre-challenge with sublethal paraquat and menadione alters the tolerance to ofloxacin and meropenem in wild-type P. aeruginosa and mutants lacking superoxide dismutase (SOD) activity (sodAB), the paraquat responsive regulator soxR, (p)ppGpp signaling (relA spoT mutant), or the alternative sigma factor rpoS. We confirmed that loss of SOD activity impairs ofloxacin and meropenem tolerance in stationary phase cells, and found that sublethal superoxide generators induce drug tolerance by stimulating SOD activity. This response is rapid, requires de novo protein synthesis, and is RpoS-dependent but does not require (p)ppGpp signaling nor SoxR. We further showed that pre-challenge with sublethal paraquat induces a SOD-dependent reduction in cell-envelope permeability and ofloxacin penetration. Our results highlight a novel mechanism of hormetic protection by superoxide generators, which may have important implications for stress-induced antibiotic tolerance in P. aeruginosa cells.

The Contribution of Environment to Impair Re‐Innervation in Age‐Related Failure of Muscle Regeneration Following Injury

An age‐related decline in the structure and function of the neuromuscular junction (NMJ) has been hypothesised to play an important role in the loss of muscle mass and force generating capacity that occurs during ageing and to contribute to the incomplete regeneration of skeletal muscle following damage.The aim of this study was to determine the relative levels of innervation of muscle fibres from adult and old wild type (WT) mice and in mice lacking superoxide dismutase (SOD1) SodKO mice prior to and during regeneration following extensive muscle damage induced by barium chloride (BaCl2). Based on the known role of environment as a contributor to the success of muscle regeneration, an additional aim was to test whether the deficits in innervation, muscle mass, and force generation seen in muscles of old mice was evident in muscles transplanted from old donors into adult hosts and vice versa.Male B6.Cg‐Tg (Thy1‐YFP) mice aged 8–10 months (adult) or 24 months (old), male adult (8–10 months) mice lacking SOD1 (C57Bl/6 Sod1KO mice) and male adult SOD1KO mice crossed with Thy1‐CFP (SOD1KO‐CFP) were used for the BaCl2 study. Mice were anaesthestised and the extensor digitorum longus (EDL) muscle was injected with 50ul BaCl2, (1.2% wt/vol in sterile saline). Adult and old WT mice were allowed to recover for up to 60 days. SOD1KO mice were studied prior to‐ and at 28 days post damage, the time point where failure in recovery of contractile force was seen in old WT mice.Male WT adult (6–8 months) and old (22 – 24 months) mice were used for the muscle transplant studies. EDL muscles were transferred to the new host, where the tendons were hen repaired and the nerve from the host implanted into the transplanted muscle. At 28 and 60 days following transplantation, mice were culled and EDL muscles were removed, contractile function measured and NMJ structure examined.For analysis of NMJ structure the post‐synaptic regions of fixed EDL muscles were stained with alpha‐bungarotoxin and Dapi. Multiple images were collected from each muscle and the innervation status of each NMJ was assessed.Data demonstrated that although the 30% full denervation of NMJ structure in association with some reduction in fibre diameter may be responsible for the 35% muscle force deficit that occurred in mice that lack SOD1, the level of denervation could not solely explain the substantial force deficit in muscle from old WT mice following extensive damage and regeneration. In contrast, data support the conclusion that the deficit in force seen in muscles from old WT mice following regeneration from damage is caused by the environment in which the muscle regenerated since transplantation of EDL muscles from either adult or old mice into old mice leads to defective regeneration of those muscles; however, experiments aimed at determining whether the environment impacted the effectiveness of re‐innervation remained inconclusive with substantial disruption evident in all instances.Support or Funding InformationWith thanks to National Institute of Ageing (AG051442) and University of Liverpool for their support.

Black sesame pigment extract from sesame dregs by subcritical CO2: Extraction optimization, composition analysis, binding copper and antioxidant protection

Black sesame pigment (BSP) is a natural product with good bioactivity. The massive accumulation of sesame dregs (SDs) from sesame seed processing provides a rich source of BSP. This study investigates the activity of BSP derived from SDs. A BSP yield of 3.58 ± 0.08% was achieved via extraction with subcritical CO2 under optimal conditions. BSP effectively bound Cu in vitro at a pH of 7.0 (R > 90%). Furthermore, binding activity was observed in Saccharomyces cerevisiae (43.78% reduction in intracellular Cu, BSP at 200 μg/mL). In addition, BSP conferred antioxidant protection in mutant yeast strains lacking superoxide dismutase and glutathione synthase by decreasing lipid peroxidation and reactive oxygen species (ROS). Superoxide dismutase and glutathione synthase protect against ROS by decreasing lipid peroxidation conferred by BSP. For decreasing intracellular ROS, only glutathione synthase seemed to be involved.

Homeobox, Wnt, and Fibroblast Growth Factor Signaling is Augmented During Alveogenesis in Mice Lacking Superoxide Dismutase 3, Extracellular

Superoxide dismutase 3, extracellular (SOD3) polymorphisms have been implicated in reduced pulmonary function development and altered risk for chronic obstructive pulmonary disease. We previously reported that gene-targeted Sod3-/- mice have impaired lung function and human SOD3 variants are associated with reduced pulmonary function in children. Reduced lung SOD3 levels were reported in mice with lower lung function with the greatest difference occurring during alveogenesis phase [postnatal (P) days 14-28]. Interactions between homeobox (HOX), wingless-type MMTV integration site member (WNT), and fibroblast growth factor (FGF) signaling govern complex developmental processes in several organs. A subset of HOX family members, HOXA5 and HOXB5, is expressed in the developing lung. Therefore, in this study we assessed the transcript expression of these family members and their downstream targets in Sod3-/- mice during alveogenesis (P14). In the lung of Sod3-/- mice, Hoxa5 and Hoxb5 increased. These transcription factors regulate WNT gene expression and were accompanied by increases in their downstream targets Wnt2 and Wnt5A, canonical and noncanonical WNT members, respectively. The WNT signaling target, lymphoid enhancer binding factor 1 (Lef1), also increased along with its downstream targets Fgf2, Fgf7, and Fgf10 in the lungs of Sod3-/- mice. Due to limited knowledge on the role of FGF2 in lung development, we further examined FGF2 protein and found increased levels in the bronchial and alveolar type II epithelial cells of Sod3-/- mice compared to age-matched controls. Thus, our findings suggest that deficient management of extracellular superoxide can lead to altered lung developmental signaling during alveogenesis in mice.

SodC modulates ras and PKB signaling in Dictyostelium

We have previously reported that the basal RasG activity is aberrantly high in cells lacking Superoxide dismutase C (SodC). Here we report that other Ras proteins such as RasC and RasD activities are not affected in sodC− cells and mutagenesis studies showed that the presence of the Cys118 in the Ras proteins is essential for the superoxide-mediated activation of Ras proteins in Dictyostelium. In addition to the loss of SodC, lack of extracellular magnesium ions increased the level of intracellular superoxide and active RasG proteins. Aberrantly active Ras proteins in sodC− cells persistently localized at the plasma membrane, but those in wild type cells under magnesium deficient medium exhibited intracellular vesicular localization. Interestingly, the aberrantly activated Ras proteins in wild type cells were largely insulated from their normal downstream events such as Phosphatidylinositol-3,4,5-P3 (PIP3) accumulation, Protein Kinase B (PKB) activation, and PKBs substrates phosphorylation. Intriguingly, however, aberrantly activated Ras proteins in sodC− cells were still engaged in signaling to their downstream targets, and thus excessive PKBs substrates phosphorylation persisted. In summary, we suggest that SodC and RasG proteins are essential part of a novel inhibitory mechanism that discourages oxidatively stressed cells from chemotaxis and thus inhibits the delivery of potentially damaged genome to the next generation.

Genetic Diversity as Consequence of a Microaerobic and Neutrophilic Lifestyle.

As a neutrophilic bacterium, Helicobacter pylori is growth deficient under extreme acidic conditions. The gastric pathogen is equipped with an acid survival kit, regulating urease activity by a pH-gated urea channel, opening below pH 6.5. After overcoming acid stress, the bacterium’s multiplication site is situated at the gastric mucosa with near neutral pH. The pathogen exhibits exceptional genetic variability, mainly due to its capability of natural transformation, termed competence. Using single cell analysis, we show here that competence is highly regulated in H. pylori. DNA uptake complex activity was reversibly shut down below pH 6.5. pH values above 6.5 opened a competence window, in which competence development was triggered by the combination of pH increase and oxidative stress. In contrast, addition of sublethal concentrations of the DNA-damaging agents ciprofloxacin or mitomycin C did not trigger competence development under our conditions. An oxygen-sensitive mutant lacking superoxide dismutase (sodB) displayed a higher competent fraction of cells than the wild type under comparable conditions. In addition, the sodB mutant was dependent on adenine for growth in broth and turned into non-cultivable coccoid forms in its absence, indicating that adenine had radical quenching capacity. Quantification of periplasmically located DNA in competent wild type cells revealed outstanding median imported DNA amounts of around 350 kb per cell within 10 min of import, with maximally a chromosomal equivalent (1.6 Mb) in individual cells, far exceeding previous amounts detected in other Gram-negative bacteria. We conclude that the pathogen’s high genetic diversity is a consequence of its enormous DNA uptake capacity, triggered by intrinsic and extrinsic oxidative stress once a neutral pH at the site of chronic host colonization allows competence development.

Catalase Enhances Growth and Biofilm Production of Mycoplasma pneumoniae.

Mycoplasma pneumoniae causes chronic respiratory disease in humans. Factors thought to be important for colonization include the ability of the mycoplasma to form a biofilm on epithelial surfaces and the production of hydrogen peroxide to damage host tissue. Almost all of the mycoplasmas, including M. pneumoniae, lack superoxide dismutase and catalase and a balance should exist between peroxide production and growth. We show here that the addition of catalase to cultures enhanced the formation of biofilms and altered the structure. The incorporation of catalase in agar increased the number of colony-forming units detected and hence could improve the clinical diagnosis of mycoplasmal diseases.

Redundant Catalases Detoxify Phagocyte Reactive Oxygen and Facilitate Histoplasma capsulatum Pathogenesis

Histoplasma capsulatum is a respiratory pathogen that infects phagocytic cells. The mechanisms allowing Histoplasma to overcome toxic reactive oxygen molecules produced by the innate immune system are an integral part of Histoplasma's ability to survive during infection. To probe the contribution of Histoplasma catalases in oxidative stress defense, we created and analyzed the virulence defects of mutants lacking CatB and CatP, which are responsible for extracellular and intracellular catalase activities, respectively. Both CatB and CatP protected Histoplasma from peroxide challenge in vitro and from antimicrobial reactive oxygen produced by human neutrophils and activated macrophages. Optimal protection required both catalases, as the survival of a double mutant lacking both CatB and CatP was lower than that of single-catalase-deficient cells. Although CatB contributed to reactive oxygen species defenses in vitro, CatB was dispensable for lung infection and extrapulmonary dissemination in vivo. Loss of CatB from a strain also lacking superoxide dismutase (Sod3) did not further reduce the survival of Histoplasma yeasts. Nevertheless, some catalase function was required for pathogenesis since simultaneous loss of both CatB and CatP attenuated Histoplasma virulence in vivo. These results demonstrate that Histoplasma's dual catalases comprise a system that enables Histoplasma to efficiently overcome the reactive oxygen produced by the innate immune system.

Cellular Responses of Candida albicans to Phagocytosis and the Extracellular Activities of Neutrophils Are Critical to Counteract Carbohydrate Starvation, Oxidative and Nitrosative Stress

Neutrophils are key players during Candida albicans infection. However, the relative contributions of neutrophil activities to fungal clearance and the relative importance of the fungal responses that counteract these activities remain unclear. We studied the contributions of the intra- and extracellular antifungal activities of human neutrophils using diagnostic Green Fluorescent Protein (GFP)-marked C. albicans strains. We found that a carbohydrate starvation response, as indicated by up-regulation of glyoxylate cycle genes, was only induced upon phagocytosis of the fungus. Similarly, the nitrosative stress response was only observed in internalised fungal cells. In contrast, the response to oxidative stress was observed in both phagocytosed and non-phagocytosed fungal cells, indicating that oxidative stress is imposed both intra- and extracellularly. We assessed the contributions of carbohydrate starvation, oxidative and nitrosative stress as antifungal activities by analysing the resistance to neutrophil killing of C. albicans mutants lacking key glyoxylate cycle, oxidative and nitrosative stress genes. We found that the glyoxylate cycle plays a crucial role in fungal resistance against neutrophils. The inability to respond to oxidative stress (in cells lacking superoxide dismutase 5 or glutathione reductase 2) renders C. albicans susceptible to neutrophil killing, due to the accumulation of reactive oxygen species (ROS). We also show that neutrophil-derived nitric oxide is crucial for the killing of C. albicans: a yhb1Δ/Δ mutant, unable to detoxify NO•, was more susceptible to neutrophils, and this phenotype was rescued by the nitric oxide scavenger carboxy-PTIO. The stress responses of C. albicans to neutrophils are partially regulated via the stress regulator Hog1 since a hog1Δ/Δ mutant was clearly less resistant to neutrophils and unable to respond properly to neutrophil-derived attack. Our data indicate that an appropriate fungal response to all three antifungal activities, carbohydrate starvation, nitrosative stress and oxidative stress, is essential for full wild type resistance to neutrophils.

Fumarate reductase is a major contributor to the generation of reactive oxygen species in the anaerobe Bacteroides fragilis

Despite the detrimental role that endogenously generated reactive oxygen species (ROS) may play in bacteria exposed to aerobic environments, very few sources of ROS have been identified in vivo. Such studies are often precluded by the presence of efficient ROS-scavenging pathways, like those found in the aerotolerant anaerobe Bacteroides fragilis. Here we demonstrate that deletion of the genes encoding catalase (Kat), alkylhydroperoxide reductase (AhpC) and thioredoxin-dependent peroxidase (Tpx) strongly inhibits H(2)O(2) detoxification in B. fragilis, thereby allowing for the quantification of ROS production. Exogenous fumarate significantly reduced H(2)O(2) production in a ΔahpCΔkatΔtpx B. fragilis strain, as did deletion of fumarate reductase subunit c (frdC). Deletion of frdC also increased the aerotolerance of a strain lacking superoxide dismutase, indicating that fumarate reductase is a major contributor to ROS formation in B. fragilis exposed to oxygen.

Effects of Memantine, a Non-Competitive N-Methyl-d-Aspartate Receptor Antagonist, on Genomic Stability

Memantine is an aminoadamantane drug useful in neurodegenerative diseases, with beneficial effects on cognitive functions. Some studies have shown that memantine protects brain cells, thereby decreasing glutamate excitotoxicity. This study evaluated the genotoxic/antigenotoxic and mutagenic effects of memantine in CF-1 mice, following standardized protocols. Memantine was administered i.p. at 7.5, 15 or 30 mg/kg for three consecutive days. Blood and brain samples were collected to assess DNA damage using the alkaline comet assay. The mutagenic effect was assessed using the bone marrow micronucleus test. In addition, possible antioxidant effects were evaluated measuring the survival of Saccharomyces cerevisiae yeast strains [wild-type (WT) and isogenic mutants lacking superoxide dismutase] to cotreatment of memantine plus hydrogen peroxide. Memantine decreased DNA oxidative damage mainly in brain tissue. This antigenotoxic effect corroborated an increase observed in the survival of S. cerevisiae WT strain against hydrogen peroxide-induced damage. Furthermore, memantine did not increase the micronucleus frequency. The overall results indicate that memantine showed no mutagenic activity, did not cause DNA damage in the blood and brain tissues and showed antigenotoxic effects in brain tissue.

Manganous Phosphate Acts as a Superoxide Dismutase

A substantial body of evidence indicates that high intracellular concentrations of inorganic manganous ions render some cells resistant to ionizing radiation and provide substantial antioxidant protection to aerobic cells lacking superoxide dismutase (SOD) enzymes. We found that manganous phosphate is unique among those manganous salts studied in its ability to remove superoxide rapidly and catalytically from aqueous solution via a disproportionation mechanism that is entirely different from those of the SOD enzymes.

Only one of a wide assortment of manganese-containing SOD mimicking compounds rescues the slow aerobic growth phenotypes of both Escherichia coli and Saccharomyces cerevisiae strains lacking superoxide dismutase enzymes

A variety of manganese-containing coordination compounds, frequently termed superoxide dismutase (SOD) mimics, have been reported to have SOD activity in vitro and to be effective at improving conditions related to increased oxidative stress in multicellular organisms. We tested the effectiveness of several of these compounds in substituting for authentic SOD enzymes in two simple systems – the prokaryote Escherichia coli and the single-celled eukaryote, Saccharomyces cerevisiae – where strains are available that completely lack cytoplasmic SOD activity and are thus significantly impaired in their ability to grow aerobically. Most of the compounds tested, including Euk-8 and Euk-134, manganese salen derivatives developed by Eukarion; M40403, a manganese complex of a bis(cyclohexylpyridine)-substituted macrocyclic ligand developed by Metaphore; and several manganese porphyrin derivatives, were ineffective in both systems. Only the manganese tetrapyridyl porphyrin complex MnTM-2-PyP and two close relatives were effective in rescuing aerobic growth of E. coli lacking SOD, and, in the case of sod1Δ yeast, only MnTM-2-PyP itself was fully effective. Surprisingly, several compounds reported to be beneficial in other in vivo model systems (Euk-8, Euk-134, M40403) were actually toxic to these organisms lacking SOD, although they had no effect on the wild-type parent strains. Our results suggest the possibility that the beneficial effects of some of the so-called “SOD mimic drugs” may be due to some property other than in vivo superoxide dismutase activity.

Mitochondrial Oxidative Stress Causes Hyperphosphorylation of Tau

Age-related neurodegenerative disease has been mechanistically linked with mitochondrial dysfunction via damage from reactive oxygen species produced within the cell. We determined whether increased mitochondrial oxidative stress could modulate or regulate two of the key neurochemical hallmarks of Alzheimer's disease (AD): tau phosphorylation, and ß-amyloid deposition. Mice lacking superoxide dismutase 2 (SOD2) die within the first week of life, and develop a complex heterogeneous phenotype arising from mitochondrial dysfunction and oxidative stress. Treatment of these mice with catalytic antioxidants increases their lifespan and rescues the peripheral phenotypes, while uncovering central nervous system pathology. We examined sod2 null mice differentially treated with high and low doses of a catalytic antioxidant and observed striking elevations in the levels of tau phosphorylation (at Ser-396 and other phospho-epitopes of tau) in the low-dose antioxidant treated mice at AD-associated residues. This hyperphosphorylation of tau was prevented with an increased dose of the antioxidant, previously reported to be sufficient to prevent neuropathology. We then genetically combined a well-characterized mouse model of AD (Tg2576) with heterozygous sod2 knockout mice to study the interactions between mitochondrial oxidative stress and cerebral Aß load. We found that mitochondrial SOD2 deficiency exacerbates amyloid burden and significantly reduces metal levels in the brain, while increasing levels of Ser-396 phosphorylated tau. These findings mechanistically link mitochondrial oxidative stress with the pathological features of AD.

Yeast flavohemoglobin is upregulated by reactive oxygen species and protects SOD mutants from nitrosative stress

Yeast flavohemoglobin (YHb) is a nitric-oxide oxidoreductase expressed in Saccharomyces cerevisiae. Previous studies have shown that YHb protects cells against nitrosative stress, but its role in protecting cells against oxidative stress is controversial. Mutants lacking superoxide dismutase (SOD1 and SOD2) have approximately seven-fold higher levels of YHb compared to wild-type cells. Levels of YHb in sod1/ sod2 mutants are reduced to that of wild-type cells when sod1/sod2 mutants are treated with the antioxidant glutathione. Surprisingly however, mutants lacking YHb1, SOD1 and SOD2 show enhanced growth rates, and reduced levels of protein oxidation compared to mutants lacking only SOD1 and SOD2. High levels of YHb in sod1/sod2 mutants may be important for protecting these mutants from enhanced nitrosative stress, as these cells are more sensitive to the NO-donor DETA-NO compared to wild-type cells. Similarly, respiring wild-type cells that are producing reactive oxygen species (ROS) from the respiratory chain, are more sensitive to DETA-NO compared to fermenting cells. Together these data suggest that elevated levels of ROS induce the expression of YHb required to protect cells against an increased sensitivity to nitrosative stress when ROS levels are increased. Supported by the American Heart Association (Beginning Grant-in-Aid) to KOB.

Cigarette smoke extract induces changes in growth and gene expression of Saccharomyces cerevisiae

The response of Saccharomyces cerevisiae cells to an aqueous extract of cigarette smoke was studied. Exposure to cigarette smoke extract inhibits yeast growth and results in global changes in gene expression spanning many functional classes of genes. Genes involved in response to oxidative stress are upregulated after a brief exposure to cigarette smoke extract. The effects of cigarette smoke extract on yeast growth can be reversed by treatment with anti-oxidants. Mutants lacking superoxide dismutase gene were hypersensitive to cigarette smoke exposure. YAP1 is a central transcriptional regulator of oxidative stress in yeast. YAP1 dependent expression of β-galactosidase was enhanced following exposure to cigarette smoke. The overall agreement between our observations and the recently reported effects of cigarette smoke on gene expression in rodent and human cells suggests that yeast can be used as a model system in toxicogenomics studies for monitoring toxic agents and studying the cellular and molecular consequences of exposure to potentially toxic agents.

Triosephosphates are toxic to superoxide dismutase-deficient Escherichia coli.

Increase in the production of triosephosphates has been considered an important factor leading to diabetic complications. It might be expected that like the other short chain monosaccharides, triosephosphates autoxidize producing superoxide radical and alpha,beta-diketones. Since superoxide can also initiate the oxidation of short chain sugars, free radical chain reactions are possible. If such reactions occur in vivo, triosephosphates would be more deleterious to cells lacking superoxide dismutase (SOD) than to normal cells. Here we demonstrate that triosephosphates kill a SOD-deficient Escherichia coli mutant much more than the parental, SOD-proficient strain. The effect is oxygen-dependent and is partially suppressed by aminoguanidine. Increased production of superoxide and diketones appeared to be the cause of triosephosphates toxicity.